This invention relates to the field of calibration devices and methods. More specifically, it relates to calibration systems for use in factory, industrial, medical and similar environments where there is a need to take accurate measurements involving fluids, such as air, oxygen and other gases. In many industrial applications involving pollution monitoring and process control the flow rate of a fluid and, in particular, a gas must be known to a high degree of accuracy. For that reason it is often necessary to calibrate the pump which produces the flow.
It is known to calibrate pump units using devices which are commonly referred to as bubble tubes. Soap bubbles are formed in an elongate, open ended glass tube having calibration marks thereon. The pump to be calibrated is connected to one end of the tube and the movement of the bubble in the tube as a function of time is a measure of the flow rate of the device under test.
These devices are not entirely satisfactory for a number of reasons, such as the requirement for a series of different sized tubes to accommodate different flow rate ranges, the difficulty of generating the soap bubbles and the frustration when bubbles break during measurement. Further, such measurement apparatus are messy, time consuming and not as portable as might be desired.
It is accordingly an object of the present invention to provide a new method and apparatus for calibrating the flow rate of pumps and similar devices.
It is another object of the invention to provide a method and apparatus which employ a critical orifice to precisely measure flow rates.
A further object of the invention is to provide a fluid receptacle which can be substantially completely evacuated during testing to insure accurate measurement.
A further object of the invention is to provide a portable, accurate pump calibration system which can measure the flow rate of pumps over a wide range without adjustments to measuring apparatus.
Another object of the invention is to provide an apparatus and method which fill a receptacle with a precise known volume and then accurately and automatically measure the time required to evacuate the receptacle thereby to obtain a measurement of the flow rate.
A further object is to integrate unknown flow rates over a period of time to obtain accurate results.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.